Most of the time when I'm out I'm shooting, my camera is in Av mode. I've selected the aperture size I want and I'm letting the camera decide on the correct shutter speed and ISO that are required to correctly expose the scene (the camera is on auto ISO with a max selected in the menu).

Obviously I want the lowest ISO possible with a shutter speed that's not likely to result in blur from the motion of the camera. Newer lenses have IS that provides several stops of stabilization; if the camera takes this into account, it could select a slower shutter speed and a lower ISO while maintaining the same exposure.

So, does the camera take this into account? I'm thinking if it doesn't, then it must be possible to get less-noisy images by setting the camera to manual and reducing the shutter speed and ISO slightly based on the cameras previous selections.

My Nikon has a several settings: minimum shutter speed (if you set to 1/30th then it will reduce down to 1/30th before starting to raise ISO). Maximum ISO (will raise ISO to this level before resuming dropping the shutter speed. If your Canon doesn't have these sorts of settings then it will try to make a sensible call. I would guess that it doesn't take into account the IS. You could confirm that by switching it on and off and doing some tests.
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MikeWJul 20 '11 at 20:55

Both Nikon and Olympus work by specifying the minimum shutter-speed. Pentax works be specifying Slow, Standard or Fast which maintains a different shutter-speed depending on the focal-length. I do not know of any maker who uses stabilization to decide on which shutter-speed is can use.
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ItaiJul 20 '11 at 21:14

I'm not going to make this an answer, but I wouldn't be surprised if it did. I know that program mode on many cameras will take the focal length of the lens into account, and aim to beat the 1/f rule. Since Av with auto ISO is a program mode (you've got two variables free), it really wouldn't surprise me if the camera dropped shutter speed in certain situations if the lens had stabilization.
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Evan KrallJul 21 '11 at 7:21

3 Answers
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I can't speak for what a particular make/model does, but a camera shouldn't take IS into account when choosing a shutter speed. This is because the camera doesn't know if you're shooting a moving subject or not.

If you're using a 24mm zoom with a three stop stabiliser the camera could potentially choose a shutter speed of 1/3s which would be fine for a still life, but if shooting people would almost certainly result in motion blur of the subject.

Shooting in Av is always prone to subject blur though isn't it same as program or full auto? If you're handing the camera control of shutter speed then that's a risk you take. If you want control over subject motion shouldn't you be using shutter priority or full manual mode?
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ChrisFletcherJul 20 '11 at 21:53

To an extent, yes but the point is that unless you're using an ultrawide the speeds provided by the 1/f rule will usually be fast enough to prevent subject blur throw IS into the mix and you suddenly have speeds 8x slower which on some lenses moves you into the very-likely-to-get-a-blurred-subject-territory
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Matt GrumJul 20 '11 at 21:56

A note on comment by @ChrisFletcher - subject blur and blur due to camera movement are two distinct causes of blur in the photo. Nothing can help you deal with subject blur, except for nailing the subject down, increasing shutter speed or effectively panning. The original question is about IS, which suggests that the poster wanted to know how to mitigate blur due to camera movement. In fact, since IS allows you to shoot at a slower shutter speed, it makes any subject blur worse!
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Martin KrzywinskiJul 20 '11 at 22:05

@Matt Grum- I'm following you now, you're saying taking IS into account means the camera could put you in a situation where you're getting worse shots than if it doesn't, because the camera doesn't know the amount of subject motion that exists? I suppose my only option in this case would be to use manual mode because I have a superior understanding of the scene?
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ChrisFletcherJul 20 '11 at 22:37

No, the camera does not take any image stabilization into account during metering. This makes sense since IS does not affect the exposure of the image, only mitigates blur.

What you describe is a putative hand-held shutter speed priority, in which the shutter speed never drops below 1/f in seconds (f = focal length of lens in mm), corrected for benefits afforded by IS. As far as I know, there isn't such a mode.

The questioner mentions shooting in Av mode with auto-ISO. So whilst IS doesn't affect the amount of incoming light knowing the lens has IS the camera could choose a longer shutter speed in order to shoot at a lower ISO.
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Matt GrumJul 20 '11 at 21:41

As far as I'm aware the camera does not pick up the IS when calculating the exposure or metering. The IS is a different aspect which is not considered by the camera when setting up a shot, it is only for ensuring a sharp shot. Some companies are starting to make bodies with IS, however this IS would not affect the technical aspect of the shot only reduce the shake.